This invention generally relates to a flow rate sensor also known as a dry flow sensor, and particularly such a sensor for use in measuring the flow rate of pelleted, granular or powdered materials such as, for example, flour, soybeans, cement, and others too numerous to mention.
Dry flow sensors of this type are known in the art and generally consist of an angular deflection plate mounted at the end of an arm, which plate is placed in the flow path of the material to be metered. The other end of the arm is mounted to a support structure using some pivotal arrangement such as a torsion pin which allows the arm to swing only about an axis parallel to the direction of material flow. Since the deflection plate is mounted at an angle in the flow path of the material, the flow of the material against the deflection plate produces normal and parallel component forces. Since the arm is limited to only movement about the parallel axis, the vertical forces have no effect while the amount of deflection in the arm about the parallel axis is proportional to the flow rate of the material. Thus, the flow rate is measured in response to the degree of deflection of the deflection plate and arm.
The accuracy of these devices are dependent on the ability to translate the flow of the material into a pivotal deflection with a minimum of tolerance, so that the design and structure of the pivotal arrangement for mounting the arm to the support becomes critical. A standard pivot pin arrangement, while relatively inexpensive, possesses more play or tolerance than is desirable, adversely affecting the accuracy of the readings. Other hinge arrangements have been used with success, but they are relatively complex and expensive. These include the use of a torsion pin of a type manufactured by Bendix Corporation.
This invention represents an improvement over these prior art sensors and particularly over the pivotally mounting arrangement for the deflection arm.
Generally, the sensor of this invention comprises an angled deflection plate mounted at the end of an arm, the other end of which is pivotally mounted to a support structure. The pivotally mounting arrangement generally includes a shim of thin gauge material such as stainless steel which is held firmly attached to the arm and to the support structure such that the shim is allowed to deflect within its elastic limits over a section thereof, whereby the arm is held firmly against horizontal and vertical movement but is allowed limited pivotal movement. The shim is relatively free in its hinge action and also provides a spring return force for the arm. Means, such as a dash pot or the like, are provided to dampen the pivotal movement of the arm, and further means, such as a transducer, are provided for translating the degree of pivotal movement of the arm into a flow rate indication.
Thus, it is a primary object of this invention to provide an improved dry flow sensor where flow rate is proportional to the degree of pivotal deflection of an arm member, with an improved pivotal mounting arrangement for the arm which minimizes horizontal and vertical movements of the arm and hence increases the accuracy and sensitivity of the sensor and which is relatively friction free and provides a spring return force for the arm .